1. Field of the Invention
The present invention relates to a movable chair backrest composed of an upper board and a lower board connected by a resilient sheet. The upper board is pivotally attached to a front of a backrest frame, and the lower board is attached to the backrest frame with a bouncing board. Thus, the chair backrest operationally deforms according to the user's back curve to provide a buffer efficiency.
2. Description of Related Art
In the structure of a chair, the backrest is important in design to support the body back. Moreover, to improve the comfort level, design for human body engineering is indispensable.
In the conventional art of chair design, an adjuster is secured inside the backrest to adjust. Although the backrest can be changed, by operating the adjuster, to make the chair fit to different users' backs having different sizes, a user has to sit in a certain posture to obtain the benefit of body engineering. When the user changes posture, the backrest after adjusting cannot provide comfortable support, because the backrest is fixed and has no corresponding adjustment immediately. Therefore, the adjuster is important to users and is operated frequently to keep the chair comfortable. Not only is the operation of the adjuster frequent and troublesome, but, also, the adjuster will malfunction often. If not controlling the adjuster, the user easily gets tired after sitting on the chair for a long duration. Such drawbacks are attributable so that the user has to adjust the conventional chair often.